1. Field of the Invention
The present invention relates to a zoom lens suitable, for example, for an image-pickup optical system for an image-pickup apparatus, such as a digital still camera and a video camera.
2. Description of the Related Art
A small and wide angle-of-view zoom lens is demanded for an image-pickup optical system for an image-pickup apparatus. A negative lead type zoom lens is known as a wide angle-of-view zoom lens in which a lens unit having a negative refractive power is arranged on a side closest to the object.
Japanese Patent Laid-Open No. (“JP”) 2005-106878 discloses a zoom lens that includes a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a negative refractive power, and has an angle of view of 120° at a wide angle end and a zoom ratio of about 2.
JP 2008-046208 discloses a zoom lens that includes a first lens unit having a negative refractive power, a second lens unit of a positive refractive power, a third lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power, and an angle of view of 106° at a wide angle end and a zoom ratio of about 2.1.
JP 2008-233284 includes a zoom lens that includes a first lens unit having a negative refractive power and a second lens unit having a positive refractive power, and has an angle of view of 113° at a wide angle end and a zoom ratio of about 1.7°.
U.S. Patent Publication No. (“US”) 2011/0109974 discloses a fixed focal length lens (single focus lens) having an angle of view of about 127°.
In order to realize a small and wide angle-of-view zoom lens having a well-corrected distortion, it is important to properly set a lens structure of each lens, a refractive power of each lens unit, a zoom type etc. For example, in order to lessen the distortion utilizing an aspheric lens, it is important to properly set a position of an aspheric surface, a lens surface shape to which the aspheric shape is applied, and an aspheric amount, etc. in an optical system. The aspheric amount being, for example, a value describing the maximum deviation from a reference spherical surface in the normal direction. The reference spherical surface being the spherical surface that passes through a surface vertex and outermost circumferential part of a light effective diameter.